1. Field of the Invention
This invention relates generally to an energy subtraction imaging system, an X-ray imaging apparatus, and a computer readable recording medium, more specifically, an energy subtraction imaging system, an X-ray imaging apparatus and a computer readable recording medium having instructions executable by a computer to execute an energy subtraction radiographic imaging method.
2. Description of the Related Art
Radiation imaging apparatuses are widely used in the fields of medical diagnosis and security control system. In medical diagnosis, for example, energy subtraction radiography using the radiation imaging apparatuses can provide an X-ray image of boon selective images or tissue selective images.
The energy subtraction radiography (or dual energy projection radiography) has been investigated for decades, since the energy subtraction radiography provides a powerful tool for selectively imaging tumors or boons by subtracting two images obtained at different energy levels of X-ray. The image data are obtained from a lower energy radiograph and a higher energy radiograph taken from a body of a patient.
There are two types of energy subtraction radiography. One is based upon a single-exposure system and another is based upon a dual-exposure system.
In the single exposure system, a single exposure of X-rays is performed to the body of the patient to obtain a lower energy radiograph and a higher energy radiograph. Two phosphor plates and an energy filter are set in a cassette where the two phosphor plates are separated by the filter. To an X-ray source, one phosphor plate (a front side image plate) is located in front of the energy filter, and another phosphor plate (a rear side image plate) is located at the rear side of the energy filter. The front side image plate receives the whole energy beam of X-rays and forms a conventional X-ray image. The front side image plate and the energy filter are configured to select out lower energy photons of the X-rays so that the rear side image plate receives mostly higher energy photons of the X-rays and obtains a higher energy X-ray image.
A weighted subtraction is made between the conventional X-ray image and the higher energy X-ray image to produce a bone selective image, and a different weighted subtraction for the conventional X-ray image and the higher energy can produce a soft tissue selective image.
In dual exposure systems, first and second radiations of X-rays are sequentially performed to the body of a patient to obtain two radiographs. The two energies of the X-rays for the first and second radiations are produced by an X-ray tube biased at 60 kilovolts peak (kVp) and 120 kilovolts peak (kVp), respectively. After the first exposure, the second exposure is performed about 0.2 second after the first exposure. This delay may cause misregistration artifacts on the subtracted images because of cardiac, respiratory, bowel and patent motion.
Maintaining multiple sets of X-ray sources may increase the operating and overhead costs for medical diagnostic facility. It may also affect the efficiency of the facility by increasing the idle time of the apparatuses. Accordingly, it would be advantageous to have a single exposure energy subtraction imaging system that is capable of forming images using X-rays at different energy levels. It would be desirable for the apparatus to be simple, reliable, and capable of being used with an existing X-ray imaging system. It would be advantageous when the single exposure energy subtraction imaging system improves its image quality of signal-to-noise ratio for the real time X-ray imaging for the diagnosis.